Hi Eugenio,
thanks for the quick reply. While I was looking for an opamp to perform the impedance matching, I indeed ordered a few free samples of OPA552 (PDIP package), but I still got problems
When this opamp is used in a buffer configuration, i.e., with a short circuit between the output and the "in-" input, it generates a sinusoidal disturb at 3MHz with an amplitude of about 4 V peak to peak that is added to the input signal.
Other guys in the lab told me that probably the opamp is not internally compensated, and indeed there is a section in the datasheet that talks about using the OPA552 in low gain. In particular, figure 11 shows an inverting configuration (gain equals to -1) with a feedback network that allows to compensate the opamp, but it restricts the bandwidth of 956kHz (in addition, it is not clear to me how this value has been evaluated).
However, this is not the main problem. Setting the feedback network eliminates the disturb, but at the output of the opamp I cannot reach the correct swing. I mean that if provide as input a sine with 10V peak to peak with frequency well below the bandwidth limit, I do not have the same amplitude in the output if I measure it with a 50 ohm load.
Again, it seems to me that the configuration cannot provide the right amount of current. Looking carefully the datasheets, it is said that the maximum output current of 200mA is actually package dependent, but in the text I cannot find which package can actually drive 200mA. I would prefer to use PDIP package because it is easier for me to set the circuitry on a breadboard.
Am I correct in the analysis? Can you please suggest other alternatives to the OPA552 or a compensation circuit with a greater bandwidth?
Thanks,
Nicola